Combined generator and liquid heat exchanger unit for absorption refrigeration system



July 2, 1957 w. G. Koel-:L 2,797,556

COMBINED GENERATOR AND LIQUID HEAT EXCHANGER UNIT F'OR ABSORPTION REFRIGERATION SYSTEM Filed DSG. 2. 1952 3 Sheets-Sheet l IN EN TOR.

/ITTORNE Y July z; 1957 W G KCGEL 2,797,556

COMBINED GENERATOR ND-LIQUID HEAT EXCHANGER UNIT FOR ABSORPTION REFRIGERATION SYSTEM Filed D66. 2, 1952 5 Sheets-Sheet 2 ATTORNEY' 2,797,556 Patented July` 2, 1,957

COMBINED GENERATOR AND LIQUID HEAT EXCHANGER UNIT FOR ABSORPTION RE- FRilGERATION SYSTEM Wilhelm Georg Kogel, Stockholm, Sweden, assignor to Aktiebolaget Elektrolux, Stockholm, Sweden, a corporation of Sweden Application December 2, 1952, Serial No. 323,554

Claims priority, application Sweden December 6, 1951 6 Claims. (Cl. 62-119.5)

My invention relates to refrigeration systems of the absorption type and more particularly to such systems in which an inert gas or pressure equalizing agent is employed.

It is an object of my invention to effect improvements in systems of this type, particularly to provide a compact arrangement of a combined generator and liquid heat exchanger unit which occupies a minimum amount of space for a system of a given size or capacity, is reliable in operation and inexpensive to manufacture.

Another object of the invention is to employ a compact bundle of upright pipes which are in the immediate vicinity of one another and thermally shielded from the surroundings by common insulation to provide both the heat exchanger for absorption liquid and the vapor expulsion unit or generator.

A further object of the invention is to provide improvements in such systems for ilowing absorption liquid through the liquid heat exchanger at a rate dependent upon its capacity to exchange heat between absorption liquid rich and weak, respectively, in refrigerant.

A still further object is to provide improvements for increasing theheat exchange capacity between rich and weak absorption liquid by reducing the flow of weak absorption liquid from the vapor expulsion unit through the heat exchanger to the absorber at a rate which is dependent upon the rate at which liquid is raised by vapor lift action in the absorption liquid circuit to effect circulation thereof.

The above and other objects and advantages of the invention will be more fully understood upon reference to the following description and accompanying drawing-s forming a part Vof this specification, and of which:

Fig. l illustrates more or less diagrammatically an absorption refrigeration system of the inert gas type embodying the invention;

Figs. 2 and 3 are fragmentary views of refrigeration systems like that shown in Fig. 1 diagrammatically illustrating other embodiments of the invention; and

Fig. 4 is an enlarged fragmentary view of parts shown in Fig. 3 to illustrate details more clearly.

In the drawing I have shown my invention in connection with an absorption refrigeration system of a uniform pressure type which is well known in the art and in which an inert pressure equalizing gas is employed. Such a refrigeration system comprises a generator or vapor expulsion unit including a boiler or pipe 11 containing a refrigerant, such as ammonia, in solution in a body of absorption liquid, such as water. Heat is supplied to the boiler 11 from a heating tube or ue 12 thermally connected therewith at 14, as by welding, for example. The heating tube 12 desirably is heated by an electrical heating element (not shown) disposed within the tube 12.

The heat supplied to the boiler 11 and its contents expels refrigerant vapor out of solution and such vapor passes upwardly from the vapor expulsion unit 10 through a vapor supply to an air cooled rectifier 15 and from the latter into an air cooled condenser 16 in which it is condensed and liquefied. Liquidv refrigerant ilows from condenser 16 through conduits 17 and 18 into va cooling element or evaporator 19 in which it evaporates and diffuses into an inert pressure equalizing gas, such as hydrogen, which enters through a conduit 20. Due to evaporation of refrigerant fluid into inert gas, a refrigerating effect is produced with `consequent absorption of heat from the surroundings.

The rich gas mixture of refrigerant vapor and inert gas formed in cooling element 19 flows from the upper part thereof through a conduit 21, one passage of a gas heat exchanger 22, conduit 23 and absorber vessel 24 into the lower end of an absorber coil 25. In absorber coil 25 the rich gas mixture flows counter-current to downwardly flowing absorption liquid which enters through a conduit 25. The absorption liquid absorbs refrigerant vapor from inert gas, and inert gas weak in refrigerant flows from absorber coil 25 in a path of ilow including conduit 27, another passage of gas heat exchanger 22 and conduit 2t) into the lower part of cooling element 19.

The circulation rof gas in the gas circuit just described is due to the difference in specific weight of the columns of gas rich and weak, respectively, in refrigerant vapor. Since the column of gas rich in refrigerant vapor and owing from cooling element 19 to the absorber coil 25 is heavier than the column `of gas weak in refrigerant and owing from the absorber coil 25 to cooling element 19, a force is produced or developed within the system for causing circulation of gas in the manner described.

Absorption solution enriched in refrigerant flows from the absorber vessel 24 through a conduit 28 into the lower end of a lift tube or pump pipe 29 in thermal exchange relation with the heating tube 12 at 30, as by welding, for example. Liquid is raised by thermosiphon or vapor-liquid lift action through pipe 29 to the upper part of boiler 11. Refrigerant vapor expelled out of solution in boiler 11, together with refrigerant vapor entering through pipe 29, flows from the boiler through the vapor supply line to the condenser 16, as previously explained. The absorption liquid from which refrigerant vapor has been expelled flows from boiler 11 through the conduit 26 into the upper part `of the absorber coil 25. The circulation of absorption solution in the liquid circuit just described is effected by raising of liquid through pipe 29.

The outlet end of the condenser 16 is connected by an upper extension of conduit 18, vessel 31 and conduit' 32 to a part of the gas circuit, as at one end of gas heat exchanger 22, for example, so that any inert gas which may pass through the condenser 16 can flow into the gas circuit. Refrigerant vapor not liquefied in the condenser ows through the upper part of conduit 18 to displace inert gas in vessel 31 and force such gas through conduit 32 into the gas circuit. The effect of forcing gas into the gas circuit in this manner is to raise the total pressure in the entire system, whereby an adequate condensing pressure is obtained to insure condensation of refrigerant vapor in condenser 16.

The parts of the generator or vapor expulsion unit 1t) just described are embedded in suitable insulating material 33 retained within an upright metal casing or shell 34 having an opening at the top through which a hollow sleeve 35 extends. The sleeve 35 is in alignment with the heating tube 12 and provides a passage through the insulating material 33 to facilitate insertion and removal `of the electrical heating element into and from, respectively, the heating tube 12 which desirably is formed with a lower closed end. The sleeve 35 is held in place in any suitable manner above the heating tube 12 to provide a connecting gap 36 therebetween which thermally shields these parts from one another and at which region heat loss upwardly through the sleeve is retarded.

In the generator or vapor expulsion unit 'of Fig. l thus far described, it will be seen' that the heating tube 12, boiler 11 and pump 29 are formed of essentially vertical pipes or conduits, the'boiler andpump including straight pipe sections in heat exchange relation with a straight section `of the heating Vtube at E4 and 30, `respectively, thereby providing a compact bundle or cluster of parts taking up a minimum cross-sectional areabetween the opposing side walls of the casing 34. In such an arnangement it is possible to `obtain an analyzing effect simply by positioning the upper part of the boiler pipe 11 in spaced relation with the sleeve 3S. This is so because the concentration of refrigerant in the absorption liquid entering the upper part of pipe 11 is greater' than the refrigerant concentration of the absorption liquid in the bottom part thereof. Hence,` absorption liquid of decreasing refrigerant concentration flows downwardly in the pipe l1. The upper part` of pipe 11 may be ref ferred to as an analyzer in which vapor bubbling therethrough and expelled from solution in the boiler or lower part thereof is analyzed in passing through cooler solution having a higher refrigerant concentration, thus removing absorption liquid vapor accompanying refrigerant vapor. After being analyzed, the vapor iiows upwardly to the condenser 16 through the vapor supply line extending upwardly from the generator 10.

In order to conserve heat which is supplied to the absorption liquid in boiler pipe 11 from heating tube 12, the relatively warm absorption liquid weak in refrigerant and owing from the boiler to the upper part of absorber coil is brought into heat exchange relation with relatively cool absorption liquid rich in refrigerant and flowing from the absorber vessel 24 to the pump pipe 29.

In Iaccordance with my invention, in order to provide a combined generator and heat exchanger unit which occupies a minimum amount of space and in which heat losses are reduced to a minimum, the compact bundlelike character of the generator parts is further extended to the liquid heat exchanger which comprises the conduits 26 and 28 having upright pipe sections 26a and 28a extending vertically downward from the extreme lower ends of the boiler pipe 11 and pump pipe 29, respectively.

The straight pipe sections 26a and 28a, which form the warmest end of the liquid heat exchanger and into which weak absorption liquid at a relatively high temperature enters through connection 37 from the lower end c of boiler pipe 11, are essentially in alignment with the heating tube 12 and in the vertically extending center region of the insulating material 33. The part of pump pipe 29 heat conductively connected to the heating tube 12 may be referred to as `a vapor forming part in which vapor bubbles are formed. The internal diameter of pump pipe 29 throughout its length is sutiiciently small to prevent the vapor bubbles from freely passing liquid therein, so that lifting of liquid will be effected by vapor-liquid lift action under the influence of a liquid reaction head formed by the column of liquid extending downwardly from the liquid surface level in ab-N sorber vessel 24 to a level approximately the same as the lowest region of the thermal connection 30 of pump pipe 29 to the heating tube 12.

Hence, in Fig. l rich absorption liquid passes from the upper end of pipe section 28a at the highest possible liquid heat exchanger temperature and flows directly upward in an essentially straight ascending path of ow through a connection 38 to the lower end of pump pipe 29. This arrangement of the warm end of the liquid heat exchanger, in which the straight pipe sections 26a and 23a essentially constitute a component of the compact cluster of generator parts and together form a unit occupying a relatively small amount of i space between.

the opposing sides of the casing 34, possessses many practical advantages. These advantages include the provision of a combined generator and liquid heat exchanger unit having a relatively Vsmall horizontal crosssectional tarea. Even with the provision of such a relatively narrow unit in which the generator and liquid heat exchanger parts areA closely bundled together in a single body of insulating material, radiation heat losses are at a minimum. Further, the essentially straight `ascending path of flow for warm rich absorption liquid which is formed by the straight pipe section 28a and pipe 29 connected thereto at 38, promotes upward movement of liquid therethrough with minimum resistance offered to iiow of the warm liquid.

ln the embodiment shown in Fig. l and being described, only the liquid heat exchanger is positioned in the bottom of the casing 34. This arrangement of the liquid heat exchanger below the compact bundle of generator parts lends itself to an arrangement in which the liquid heat exchanger conduits 26 and 28 are of U-shaped form, the upright pipe sections 26:1 and 28a constituting one arm of the U-shaped loop. As shown, the pipe 26 extends concentrically within the pipe 28 with the latter forming an outer jacket of the liquid heat exchanger, the upright straight pipe sections of the U-shaped pipes 26 and 28 being joined =by bottom connecting bends which are curved along their entire extent between the upright pipe sections to which they are joined.

The straight pipe section 28b of the U-shaped loop of Conduit 2S is connected at its upper end to the bottom part of the absorber vessel 24, while the section of the conduit 26 therein passes through the entire length of the absorber vessel below the liquid surface therein and then extends upwardly to the upper end of the absorber coil 25. The rich absorption liquid entering the upper end of pipe section 28h, which constitutes the cool end of the liquid heat exchanger, immediately flows in heat exchange relation with weak absorption liquid flowing in pipe 26. While the cool end yof the liquid heat exchanger piping may be located outside the insulated casing 34, further advantages are gained from a liquid heat exchanger making use of straight pipe sections in that the absorber vessel 24 may be located in the immediate vicinity of the casing 34 and the arm or straight pipe section 28]) of the U-shaped heat exchanger loop may also be embedded in the insulating material 33. Since the pipe section 28b is in the cooler part of the liquid heat exchanger piping, objectionable heat losses do not occur even though such cooler part is located at a region removed from the vertical center of the insulating material 33.

ln the embodiment of Fig. l, the absorber vessel 24 is actually employed as an extension of pipe 28 which forms the outer passage of the liquid heat exchanger. This is so because weak absorption liquid flowing through conduit 26 in the bottom part of absorber vessel 24 and on its way to the upper` part of the absorber coil 25 passes in heat exchange relation with the body of rich absorption liquid stored and accumulated in such vessel.

ln Fig. 2 I have shown another embodiment of my invention which differs from the embodiment of Fig. l in that the electrical heating element is inserted into and removed from the generator at the bottom of the heat insulated casing, :and weak absorption liquid rather than rich absorption liquid is raised by vapor-liquid lift action in the pump pipe. In Fig. 2, in which parts similar to those shown in Fig. l are referred to by the same reference numerals, rich absorption liquid flows from absorber vessel 24 through the outer passage 28 of the liquid heat exchanger and a horizontal conduit 40 into boiler pipe 11', the rich absorption liquid entering the latter at a point 40a which is at a level below the liquid level in the absorber vessel 24 and below the surface level of the liquid column contained in the boiler.

The boiler pipe 11 is heat conductively connected at` 14' to the heating tube 12' adapted to be heated by a suitable electrical heating element. The heating tube 12' extends downwardly in the insulating material 33', the lower end thereof projecting through an opening in the bottom of the casing 34'. However, it should be understood that an arrangement may be provided which is like that shown in Fig. l' in which a sleeve 35 coopenates the heating tube.

Liquid flows fromy the bottom closed end of boiler 1-1' into the lower end of pump pipe 29', which is heat conductively connected at 30' to the heating tube 12', and liquid is raised through the pump pipe by vaporliquid lift action in'to the upper end ot an open-endedA stand'pipe or riser 41. The principal part of the generatedvapor is expelled from solutionv in boiler pipe 11', and liquid of decreasing refrigerant concentration flows downwardly tothe bottom closed end thereof into the lower end of pump pipe 29". The vapor from the upper end of the lift or pur'n'p pipe 29' enters the upper open end of the riser pipe 41 and passes into the upper closed end of ay pipe 42 which extends upwardly from and constitutes a verticall extension of the right-hand arm 28'@ of the outer U-shaped liquid heat exchanger passage. y The pipe 42 envelops the riser 41 to provide a passage of annular form therebetween through which vapor ilows downwardly, such vapor being capable yof depressing the liquid level therein so that the vapor can bubble hori-V zontally through enriched absorption liquid in the conduit 40y andl upper part of the liquid column in boiler pfipe 11'. In this way vapor bubbling through enriched absorption is analyzed, whereby absorption'y liquid vapor will be removed from refrigerant vapor. After being analyzed, suc'h vapor and vapor expelled from solution in boiler pipe 11' flow upwardly through the upper part of such pipe into the vapor supply li'ne leadingV to the condenser, in the marmer illustrated in Fig. l.

In Fig. 2 absorption liquid weak in refrigerant flows downwardly in riser pipe 41. and thence through the pipe 26' to the upper end of the absorber coil 25". The riser pipe 41 essentially constitutes a continuation or upward extension of the right-hand arm 26a of the inner U-shaped liquid heat exchanger passage. As in the embodiment of Fig. l, the pipe 26' includes a section extending through the bottom part of the absorber vessel 24' below the liquid surface level therein. In the event further cooling of the weak absorption liquid is necessary, the pipe 26' may include :a pipe section 26b forming a jacketabout conduit 23' which is similar to conduit 23 in Fig. 1 and through which relatively cool inert gas enriched inre frigerant flows from cooling element 19 to the absorber vessel. After heat exchange with enriched inert gas in conduit 23', weak absorption liquid enters the absorber coil 25' from the upper end of pipe section 26'b.

In Fig. 2 liquid is raised by vapor-liquid lift action in pump pipe 29' under the inuence of a reaction head formed by the liquid column in boiler pipe 11. However, the generator or vapor expulsion unit in Fig. 2 essentially comprises a cluster or bundle of vertical pipes including heating tube 12', boiler pripe 11', pump pipe 29', riser pipe 41, vapor conveying pipe 42, and analyzer pipe 40. As in the irst described embodiment, the upper ends of the pipe sections 26'a and 28"@ form the warm end of the liquid heat exchanger which is well embedded in the insulating material 33' and may be located even closer to the heating tube 12' than shown, it being understood that Fig. 2 diagrammatically illustrates a plan view while in actual practice the boiler pipe 11', pump 29' and straight pipe sections 26'a 'and 28'a desirably are disposed Iin circumferentially spaced apart relation about the heating tube 12' and in the immediate vicinity of the latter, thus permitting a horizontal conduit connection 40 which is considerably shorter than that shown in Fig. 2.

In view of the above explanation, it will be understood that the straight pipe sections 26a and 28'a of the liquid heat exchanger, and alsoy theA upper straight pipe extensions 41 and 42 thereof, form a component of the compact bundle or cluster of pipes to provide a combined generator and liquid heat exchanger unit embedded in a single body of insulating material 33' having the same' cross-sectional area throughout the entire vertical extent of' the casing or shell 34'. In the embodiment of Fig. 2, both the left-hand and right-hand armsy of the U-shaped liquid heat exchanger are shown embedded in the insulating material 33', each pair or straight pipe sections forming the liquid heat exchanger arms being joined by a bottom connecting bend which is curved along its entire extent between the straight pipe sections to which it is joined. Further, each liquid heat exchanger arm is as long as the height of the liquid column in boiler pipe 11' which, as previously explained, constitutes the reaction head for the pump pipe 29'. Under such conditions, a liquid heat exchanger of the type shown and described will effect adequate Vheat exchange between weak and rich absorption solutions when piping of the usual size is employed for the liquid heat exchanger. By way-of example and without limitation, piping having an internal diameter of aboutr30 mm. can be used for the piping 28' and piping having an internal diameter of about 9 mm. can be used for the piping 26'.

Another embodiment of the invention is illustrated in Figs. 3 and 4 which is like the embodiment of Fig. 2 and differs therefrom in that a vapor-liquid lift or pump is provided in which the raised liquid is split up and divided into two streams, one of which flows through the weak gas passage of the liquid heat exchanger to the absorber coil and the other of which simply returns to the inlet of the pump pipe and is recirculated by the latter. In Fig. 3, in which parts like those in Fig. 2 are designated by the same reference numerals, absorption liquid of decreasing refrigerant concentration flows downwardly in boiler 11' and is then raised by vapor-liquid action in pump pipe 29".

The upper part of pump pipe 29" in its lengthwise direction is provided with a dividing or separating wall 45, as shown in Fig. 4. The upper end of pipe 29" at opposite sides of the separating wall 45 is formed with openings 46 and 47 through which absorption liquid passes while being raised through the pipe 29" by vaporliquid lift action. Conduits 48 and 49 are connected to the pipe 29" at the regions of the openings 46 and 47, respectively, which are of a definite cross-sectional area with respect to one another for reasons which will be given presently and are substantially at the same level. Raised liquid overflowing and spilling through opening 47 passes into conduit 49 which is connected to the upper end of the riser or standpipe 41". The liquid supplied to the riser 41" flows downwardly therein and through piping 26' to the upper part of the absorber coil in the same manner as shown in Fig. 2 and previously described.

Raised liquid overflowing and spilling through opening 46 passes into conduit 43 which in turn is connected to a vertical conduit Sii. The lower end of conduit 5G is connected to the straight pipe section 2821 of the liquid heat exchanger at a region below the connection of conduit 40 thereto. Hence, liquid passing downwardly through conduit 50 flows into the outer passage of the liquid heat exchanger and mixes with rich absorption liquid ilowing from the absorber vessel 24', such liquid mixture then flowing through conduit 40 and boiler pipe 11' to the lower end of the pump pipe 29".

The upper ends of conduits 5t), 41" and 42" are connected to a common cross connection 5l into which litting vapor ilows from the outer ends of conduits 48 and 49 and upper ends of conduits 50 and 41". Vapor in the cross connection 51 ows through the vapor conveying4 conduit 42, upper part of pipe section 28a and conduit 40 into the boiler pipe 11 in the same manner vapor ows from the upper end of pump pipe 29 through conduit 42 into boiler pipe 11 in the embodiment of Fig. 2, as explained above.

In vapor-liquid pumps of the kind shown and described herein, the ratio of the quantity of weak absorption liquid being circulated to the quantity of refrigerant generated is referred to as the pumping ratio. When reliable functioning of the vapor-liquid lift pump is a primary consideration, it is desirable to provide a pumping ratio of about 6 to 8 when ammonia is employed as the refrigerant and water as the absorption liquid. When low evaporator temperature and performance are viewed as the primary consideration, a pumping ratio in the neighborhood of about 2.5 to 3.5 is more suitable. Under such conditions, excessive circulation of absorption solution through the liquid heat exchanger is avoided, the liquid heat exchanger operates more efficiently, and the absorber functions better to provide for the evaporator inert gas having the weakest possible concentration of refrigerant. t

By splitting up the absorption liquid` in the manner shown in Figs. 3 and 4 and described above, it is possible to keep recirculating a part of the absorption liquid all of the time through the pump pipe 29. In this way the raised liquid can be divided into two streams of such size that one Will give a high pumping ratio of about 6 to 8 for the pump pipe 29" while the other stream flowing to the absorber coil 25' effects circulation of weak absorption liquid at a pumping ratio in a range equivalent to about 2.5 to 3.5 providing such weak absorption liquid constituted the entire quantity of liquid raised by the pump pipe 29". The splitting of raised absorption liquid at the upper end of the pump pipe 29 is particularlyadvantageous in an absorption liquid circuit of the kind shown in Figs. 3 and 4, because the quantity of weak absorption liquid circulated through the liquid heat exchanger piping 26 can be adjusted so that the heat exchanger will operate efficiently; that is, effectively transfer heat between rich and weak absorption liquids which pass through piping 26 and 28 at such flow rates as to bring the rich absorption liquid to the highest possible temperature when leaving the heat exchanger and thereby enable the latter to operate at optimum capacity. Hence, in addition to reducing the quantity of absorption liquid flowing from vapor expulsion unit through ythe heat exchanger to the absorber which is due to expulsion of refrigerant vapor from absorption liquid in the vapor expulsion unit, the quantity of absorption liquid flowing from the vapor expulsion unit through the heat exchanger to the absorber is reduced at a rate which is dependent upon the rate at which liquid is raised by pump 29". By way of example and without limitation, satisfactory operation of an arrangement like that shown in Figs. 3 and 4 and just described has been obtained when employing piping having an internal diameter of about 20 to 24 mm. for the outer liquid heat exchanger conduit 28 and piping having an internal diameter of about to 8 mm. internal diameter for the inner liquid heat exchanger conduit 26.

in View of the foregoing, it will now be understood that, in each of the embodiments illustrated and described above, the liquid heat exchanger includes straight pipe sections which are substantially vertical and form straight ascending and descending paths of flow for absorption liquid which constitute a major part of the overall lengths of the liquid heat exchanger passages enveloped by the insulating material retained in the generator shell or casing.

Although l have shown and described particular embodiments of my invention, it will be obvious to those skilled in the art that various changes and modifications may be made, and that certain features may be employed independently of others, without departing from the spirit and scope of the invention. For example, the lower end of conduit in Fig. 3 may be connected to boiler pipe 11 at a region thereof below the connection thereto of conduit 40. I, therefore, aim in the following claims to cover all such modifications and changes as fall within the true spirit and scope of the invention.

What is claimed is:

1. In an absorption refrigeration system, a circuit for circulation of absorption liquid comprising an absorber, generator and liquid heat exchanger therebetween having passages for flowing in thermal exchange relation absorption liquid rich and weak, respectively, in refrigerant, a plurality of upright pipes having essentially straight pipe sections, common insulating means enveloping said straight pipe sections for insulating the latter from the surroundings, a heating tube including one of said straight pipe sections, said generator comprising several of said straight pipe sections which are connected in said circuit and at least two of which are substantially parallel to the straight pipe section of said heating tube and contain absorption liquid arranged to receive heat from said heating tube, said generator comprising a boiler and vapor-liquid lift tube each of which respectively includes one of said two straight pipe sections, and means forming the passages of said liquid heat exchanger including at least two pairs of said straight pipe sections, each pair of said pipe sections having a bottom connecting bend joined thereto, said last-mentioned straight pipe sections being substantially vertical and forming straight ascending and descending paths of ow for absorption liquid which, together with said connecting bends, constitute a major part of the overall lengths of the liquid heat exchanger passages enveloped by said common insulating means, said connecting bends being curved along their entire extent between said upright straight pipe sections to which they are joined.

2. An absorption refrigeration system as set forth in Iclaim 1 in which a pair of said straight pipe sections forming the passages of said liquid heat exchanger are essentially in alignment with said heating tube and extend downwardly from the vicinity of the lower end thereof.

3. An absorption refrigeration system as set forth in claim 2 in which the upper end of one of said pipe sections forming a liquid heat exchanger passage is connected to the lower end of said boiler to provide one liquid conveying line and the upper end of the other of said pipe sections forming the other liquid heat exchanger passage is connected to the lower end of said vapor-liquid lift tube to provide another liquid conveying line, each of said liquid conveying lines forming an essentially straight path of flow for absorption liquid through a vertically extending range of said insulating means.

4. An absorption refrigeration system as set forth in claim 1 in which said circuit contains a liquid column forming a reaction head under the influence of which liquid is raised by vapor-liquid lift action in said lift tube, the upper ends of at least one pair of said straight pipe sections forming the passages of said liquid heat exchanger being disposed at a region at a level which is at the vicinity of the liquid surface level of said reaction head, and the aforementioned pair of said straight pipe sections and connecting bends joined thereto extending downwardly from said region through a vertical distance which is at least as great as the height of said reaction head.

S. An absorption refrigeration system as set forth in claim 1 in which said generator pipe sections and pipe sections forming said liquid heat exchanger passages are distributed circumferentially about said heating tube and together form a compact bundle of pipes within said common insulating means.

6. An absorption refrigeration system as set forth in claim l in which said circuit for absorption liquid includes means for flowing a part of the liquid raised by said vapor-liquid lift tube in a path of flow which bypasses said liquid heat exchanger pipe section for absorption liquid weak in refrigerant and conducts such part of the liquid to the inlet of said vapor-liquid lift tube.

References Cited in the file of this patent UNITED STATES PATENTS 1,620,843 Von Platten Mar. 15, 1927 10 1,791,441 Bertsch Feb. 3, 1931 1,802,537 Roos Apr. 28, 1931 10 Altenkirch June 13, 1933 Knight Mar. 6, 1934 Kohler Aug. 18, 1936 Smith May 31, 1938 Gaugler June 6, 1944 Kogel June 18, 1946 Ashby Apr. 18, 1950 Kogel Jan. 16, 1951 FOREIGN PATENTS Great Britain Aug. 2, 1950 

